With the widespread availability of computers, computer graphics artists and animators can rely upon computers to assist in production process for creating animations and computer-generated imagery (CGI). This may include using computers to have physical models be represented by virtual models in computer memory. Typically, two-dimensional (2D) or three-dimensional (3D) computer-aided animation combines 2D/3D models of objects and programmed movement of one or more of the models. In 3D computer animation, the first step is typically the object modeling process. Virtual objects can be sculpted much like real clay or plaster, working from general forms to specific details, for example, with various sculpting tools. Models may then be constructed, for example, out of geometrical vertices, faces, and edges in a 3D coordinate system to represent the virtual objects. These models can then be manipulated using computers to, for example, simulate physics, design aesthetic actions such as poses or other deformations, crate lighting, coloring and paint, or the like, of characters or other elements of a computer animation display.
One core functional aspect of computer graphics is to convert geometric and/or mathematical descriptions of objects into images. This process is known in the industry as “rendering.” For movies, other animated features, shorts, and special effects, a user (e.g., a skilled computer graphics artist) can specify the geometric or mathematical description of objects such as characters, props, backgrounds, or the like, as models to be used in the rendered image or animation sequence. In some instances, the geometric description of an object may include a number of animation control variables (avars) and values for the avars. An animator may also pose the objects within the image or sequence and specify motions and positions of the objects over time to create an animation.
As such, the production of CGI and computer-aided animation may involve the extensive use of various computer graphics techniques to produce a visually appealing image from the geometric description of an object that may be used to convey an essential element of a story or provide a desired special effect. One of the challenges in creating these visually appealing images can be the balancing of a desire for a highly-detailed image of a character or other object with the practical issues involved in allocating the resources (both human and computational) required to produce those visually appealing images.
In particular, most characters, such as humans or animals, have some kind of hair or fur on their bodies. It has been noted that human vision is very sensitive to the appearance of hair and can detect subtle inaccuracies in its appearance. Moreover, since hair can provide a very personal expression of style and creativity, hair is often considered one of the most important customization features for avatars, such as for online social communities and gaming networks. On the other hand, rendering hair is not a trivial matter as it is computationally expensive to model the complex behavior of light scattering events in a volume of hair. While there has been much research on hair shading using physical models, it is difficult for computer graphics rendering to benefit from such research because it can be difficult for artists and other creative professionals to manipulate the rendering parameters, e.g., physical material properties such as indices of refraction and absorption coefficients, to achieve a specific aesthetic goal.
Thus, while physically based shading models can provide realistic and aesthetically pleasing results, they are often inappropriate for creative works due to their complexity. As a result, ad-hoc shaders that are computationally less expensive have become common in production use. However, such ad-hoc shaders lack the richness of detail provided by physical shaders, thereby providing a sub-optimal aesthetic appearance that may also break down in certain lighting conditions.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by providing a three-dimensional computer graphics rendering system capable of producing aesthetically pleasing results for features such as hair while providing intuitive manipulation controls for art direction.